Optimisation, design, production, and testing of a topology of an internal actuation system to deflect a seamless morphing leading edge of a wing were proposed.
The actuation system was designed using an aeroelastic optimisation code including sufficient boundary conditions, such as leading edge skin strain allowables, to ensure a practical outcome of the actuation topology. The variation in aero loading during the deflection was taken into account in order not to design the leading edge only for straight and deflected configuration, but to ensure feasibility of the system during transition. The design was translated into a working actuation system which was to be built and tested.
The result of this proposal not only delivered an optimised topology of the actuation system, which was built and tested, for the wing geometry specified by the GRA member, but also provided the ability to quickly develop new actuation architectures for alternative wing geometries.
The Leading Edge Topology Optimised Design and Demonstrator (LeaTop) project was an EU Clean Sky project. The aim of the research was to design and demonstrate the construction of a seamless morphing leading edge device that is capable of withstanding full aerodynamics loads.
Seamless morphing leading edge devices show potential to reduce noise and drag of a wing, however, practically designing and implementing these devices as an end solution within the structural constraints of modern materials proves to be a challenge. The focus of this research is on the development of a mechanism capable of morphing the leading edge with respect to a set target airfoil shape. The project uses the in-house aeroelastic tools developed for topology optimisation to generate, design and build a demonstrator that is fit for testing the system under equivalent aerodynamic loads.
It is demonstrated in the project how a concept for the leading-edge actuation system can be created. The input to the concept generation process was provided by the Green Regional Aircraft (GRA) partner Fraunhofer Gesellschaft in terms of geometry of the leading edge, loads and requirements. Based on this input, a topology was designed for the actuation system, together with skin stiffness requirements.
The result of the concept design was a layout of an actuation system and skin stiffness distribution which allowed the prescribed morphing deformations of the leading edge under a given aerodynamic load. The layout and skin were analysed using finite elements to validate their feasibility.
The parts of the kinematic system which will carry out the prescribed deformation of the morphing leading edge were milled from aluminium. The morphing skin was also made out of aluminium and was supplied by the GRA partner Fraunhofer Gesellschaft. They were also responsible for producing the spar, a complex geometry which was milled out of aluminium as well. All these parts were assembled and mounted into a test rig. This test rig was designed such that the weights, representing the aerodynamic loads, could be applied in the correct direction.
Three types of experiments were carried out:
- strain measurements in the skin to get an estimate of the strain distribution when the leading edge is locked in its cruise shape and when the leading edge is morphing into landing configuration;
- displacement measurements of the actuation system to investigate whether the actuation system is truly locked when in cruise shape;
- shape measurements of the morphing leading edge to compare to the intended morphed target shape.
The experimental results showed that the objectives of the LeaTop project were met, i.e. that the cruise shape could be preserved under cruise loads, and that a morphed target shape could be achieved.